Camera-based traffic monitoring systems have become increasingly deployed by law enforcement agencies and municipalities to enforce traffic laws and modify unsafe driving behavior, such as speeding running red lights or stop signs, and making illegal turns. The most effective programs combine consistent use of traffic cameras supported by automated processing solutions that deliver rapid ticketing of traffic violators, with other program elements including community education and specific targeted road safety initiatives like drunk-driving enforcement programs and license demerit penalties. However, many current traffic enforcement systems using photographic techniques have disadvantages that generally do not facilitate efficient automation and validation of the photographs required for effective use as legal evidence.
Digital-based red-light camera systems have come to replace traditional 35 mm analog-based cameras and photographic techniques to acquire the photographic evidence of traffic offenses. In the field of traffic enforcement technologies, capturing vehicle offense data involves a compromise between storage space requirements and image resolution. Typically, an offense is recorded as a number of still images of the vehicle together with some pertinent information such as speed, time of offense, and so on.
Red-light violation recording has traditionally been done with still cameras, either digital or wet film, or with video camera systems. These systems suffer from a number of shortcomings. For example, still images typically do not convey enough information to assess the circumstances surrounding a violation. A vehicle forced to enter an intersection after the traffic signals are red while yielding to an emergency vehicle will be shown as a violator on still images and the vehicle's driver will be prosecuted if the emergency vehicle does not appear in the still images. Also, at many intersections vehicles are permitted to turn during a red light if they first stop. Still images do not show the acceleration and speed of a vehicle and cannot determine if the vehicle has progressed unlawfully, i.e., without first stopping. For speed enforcement, vehicle speed must be determined from the vehicle detection device and imprinted on the photograph. Errors in the vehicle's detected speed will not be apparent on the photograph, as still images do not convey any impression of speed. Although multiple still photographs may be taken to show speed across two or more points, this solution results in increased image capture and storage requirements and causes the camera to be occupied for the duration of the image sequence.
Image resolution is critical to providing sufficient information to resolve important scene details such as the identifying data comprising the vehicle license (registration) plate and the driver's face. However, increasing image resolution also increases data storage requirements.
To solve the problem of providing contextual or background evidence surrounding a potential traffic offense at a photo-monitored location, video has been incorporated in some red-light traffic systems. However, the advent of video has certain significant disadvantages. Most notably, when an enforcement agency wishes to use video in their evidence set, the problems related to transmission bandwidth and data storage is significantly compounded. Digital video technology generates data at a vastly greater rate than digital still-image technology, given the same resolution. Although video footage has been used for identification and prosecution of vehicles in violation of traffic laws, the generally low resolution of present video systems makes it difficult to determine the fine details required for prosecution, such as the vehicle license plate or the features of the driver's face. The low resolution problem also requires the video camera to be close to the detected vehicle or to physically move and track the vehicle, both of which are major disadvantages when used in automated traffic monitoring systems. Although high-resolution video cameras can be employed for identification and prosecution of vehicles in violation of traffic laws, if the information from a high-resolution video camera is stored digitally, the amount of file storage required makes it difficult or impractical to store and communicate the amount of information generated. This is especially true for systems that do not provide efficient video clips, but rather shoot and transmit long loops of constant video data.
The standard start/stop capturing mechanism available in almost all video capture systems is inadequate to satisfy the requirement for providing footage both before and after the offense is detected. By the time the offense is detected it is too late to start a video capture sequence. It is also generally difficult to anticipate an offense and preemptively commence video capture. Furthermore, where the footage from a video system is recorded on magnetic tape the retrieval of information is time consuming and finding a specific violation or incident cannot be done instantaneously.